Abstract: Yangtze sturgeon (Acipenser dabryanus) is an endemic fish in China and has been listed as a critically endangered (CR) species by the International Union for Conservation of Nature (IUCN). In order to provide a reference basis for healthy breeding and disease analysis of juvenile Yangtze sturgeon, we analyzed the composition, diversity and dynamic changes of microbial flora between its surface mucus, intestinal content and culture water by using Illumina high-throughput sequencing technology. The results show the diversity of microorganisms in culture water was higher than that in mucus and intestinal content. The microbial community structure of mucus and intestinal content were more similar, and could be clearly distinguished from the microbial community of culture water. On phylum level, mucus and intestinal content were mainly composed of Actinobacteria, Proteobacteria and Firmicutes, while the culture water was mainly composed of Proteobacteria, Bacteroidetes and Firmicutes. Seven potential pathogenic genera were found, mainly in culture water and mucus which might lead to the occurrence of diseases under certain circumstances. BugBase phenotype prediction analysis reveals that both Gram negative and Gram positive bacteria were present in the mucus, intestinal content and culture water of juvenile Yangtze sturgeon. The dominant microbiota of intestinal content was Gram positive bacteria, accounting for over 60%. The dominant microbial communities in mucus and culture water were both Gram negative bacteria, accounting for 60% and 70%, respectively. In terms of oxygen demand, mucus and intestinal content were mainly composed of aerobic bacteria, while culture water was mainly composed of aerobic and facultative anaerobic bacteria.